Abstract

A two-step GaN barrier growth methodology was developed for InxGa1−xN/GaN multiple quantum wellsolar cells in which a lower temperature GaN cap layer was grown on top of the quantum wells(QWs) and then followed by a higher temperature GaN barrier layer. The performance of the solar cells improved markedly by increasing the low temperature GaN cap layer thickness from 1.5 to 3.0 nm. High-angle annular dark field scanning transmission electron microscopy and atom probe tomography measurements showed that increasing the GaN cap layer thickness improved the uniformity and increased the average indium content of the QWs.

Received 26 March 2012Accepted 30 March 2012Published online 16 April 2012

Acknowledgments:

This work was supported by the DARPA High Performance InGaN-Based Solar Cells Program (Grant No. HR0011-10-1-0049), the California Advanced Solar Technologies Institute (CAST) (Grant No. 143188), and the Solid State Lighting and Energy Center (SSLEC). R.M.F was partially supported by the Center for Energy Efficient Materials (CEEM) at UCSB, an Energy Frontier Research Center funded by the U.S. DOE (Grant No. DE-SC0001009). A portion of this work was done in the UCSB nanofabrication facility, part of the NSF NNIN network (Grant No. ECS-0335765), as well as the UCSB MRL, which is supported by the NSF MRSEC program (Grant No. DMR05-20415). The sapphire substrates and the trimethylindium metalorganic sources used for this study were provided by Namiki Precision Jewel and Sonata LLC, respectively.